A frequent goal in designing wireless communications systems is to increase the number of users that may be simultaneously served by the communications system. This may be referred to as increasing system capacity. In multiple access communications systems, including code division multiple access (CDMA) wireless communications systems, the use of adaptive antenna arrays at the base transceiver has been proposed as a method of increasing system capacity.
An adaptive array antenna includes two or more radiating elements with dimensions, spacing, orientation, and an illumination sequence that produce a field from a combination of fields emitted from individual elements that has greater intensities in some directions and lesser field intensities in other directions. An adaptive array antenna assists in increasing system capacity because this field pattern or radiation pattern of the adaptive array antenna, which includes multiple beams or lobes, may be configured such that signals intended for a selected user are in higher-gain antenna lobes pointed in the direction of a selected user, while other users likely lie in nulls of the antenna pattern. Thus system capacity increases since signals intended for other users in the selected user's antenna null are not adversely affected or degraded by the power intended for the selected user.
Configuring the antenna array or adaptive antenna array is often accomplished using a set of antenna array weights or an antenna array weighting pattern in the processing of the signal to be applied to the antenna array. In order for the adaptive antenna array to provide a performance improvement the antenna array must continually be re-configured or the antenna array weighting pattern must be updated at least often enough to account for channel variations, due for example to relative motion between the source or antenna array and the user or target antenna or antennas. Most adaptive array antenna systems or systems using adaptive arrays utilize a schema where the target receiver or subscriber unit quasi-continually measures or assesses the channel and provides feed back information that allows the source or base station to determine a proper antenna array weighting pattern that will adapt the array to current channel conditions in order to maintain an acceptable channel to the target receiver.
However, the feedback information from the target will be sent or transmitted over the same or a closely correlated channel and therefore is subject to channel induced errors in the information received at the source. Unfortunately errors in this feedback information are likely to result in errors in the antenna weighting pattern and this can dramatically and adversely affect the array performance. While there may be ways of protecting this information, such as extensive error correction coding, most or many of them represent significant and undesirable increases in system overhead or delay. Thus, it should be apparent that a need exists for a reliable method and apparatus for adapting an antenna array, preferably without increasing overhead.